1. Field of the Invention
This invention is directed to a process for preparing substantially homogeneous and stable heavy-duty liquid detergent compositions which are suitable for all-purpose cleaning.
In the detergent art it has been common practice to prepare detergent compositions in solid particulate form as, for example, by spray dying a slurry of the detergent composition. These products contain in addition to the surface-active agent and various adjuvants, alkaline builder salts such as sodium tripolyphosphate in significant amounts to improve the detergent or washing power of the composition. Particulate detergent compositions are not as versatile in use as liquid detergent compositions for a variety of known reasons and it is highly desirable therefore, to provide a heavy-duty detergent composition in liquid form.
The preparation of a stable, homogeneous heavy-duty liquid detergent however, presents many problems to the formulator since the product should be as concentrated as possible, not separate on storage, perform heavy-duty cleaning comparatively to dry products, and be as economical in usage. The most important underlying problem is to provide a detergent system having sufficient surface active ingredients and builder in a liquid system wherein none of the components will settle out or show unsightly phase separation on storage.
2. Description of the Prior Art
In heavy-duty liquid detergents the compatibility of a builder component with a detergent surfactant is poor and the builder and/or the surfactant are usually reduced in concentration to overcome any phase separation problems, but with a significantly lower detergency effectiveness. This relative insolubility of the materials is further compounded due to the lower solubility of the relatively inexpensive sodium builder salts e.g., sodium tripolyphosphate, as compared to the more expensive and highly soluble potassium salts, which are on the order of three or more times more soluble and which have consequently been preferentially employed by formulators to avoid this problem.
The formulation of a stable, homogeneous heavy-duty liquid detergent which is relatively inexpensive and easy to produce has consequently perplexed those skilled in the art over the years, and the proposed products and processes are still undesirable for a variety of reasons, including difficulty of manufacture, cost, among others. U.S. Pat. Nos. 2,733,213 and 2,733,214 disclose a detergent composition in a paste form, which is not a liquid suitable for the uses contemplated herein. As is well known the viscosity of a paste is well over 200,000 centiposes.
According to U.S. Pat. No. 2,859,182
"Heavy duty liquid detergent compositions may contain one or more synthetic detergents and a polyphosphate in an aqueous medium. However, the presence of a considerable amount of polyphosphate in these compositions causes the synthetic detergents to separate from solution at room temperature thereby making the product commercially unattractive. Hence, the major problem of preparing homogeneous heavy duty liquid detergent compositions involves the discovery of means for preventing the synthetic detergents from separating out of solution at room temperature or below in the presence of a considerable amount of polyphosphate." PA1 "TPP has a relatively low solubility in water, the Saturation concentration in water at room temperature being about 164 g/liter, corresponding to about 14 percent by weight. Such low solubility is not a disadvantage for solid detergent compositions, which may for example be in the form of powder, granules, flakes or the like. However such low solubility represents a practically insolvable problem in the formulation of homogeneous liquid detergent compositions, due to the fact that these normally require a TPP content of about 18 or 40 percent by weight as this is the level of concentration in most commercial solid detergent compositions. In fact the proportion of TPP capable of being introduced into liquid detergent compositions is substantially lower than the theoreticl 14 percent by weight (which 9 (sic) the saturation concentration of TPP) due to the presence of particularly of surface-active agents. A well-known effect is that surface-active agents and TPP have a mutual effect on their respective solubilities, the higher the concentration of surface-active agent in liquid compositions the less the solubility of TPP, and vice versa."
This patent purported to solve this problem by using a combination of an alkylolamide and a hydrotrope (such as sodium toluene sulfonate) together with the highly soluble and expensive potassium detergent salts and builder salts; neither the alkylolamide nor the hydrotrope was effective by itself.
According to U.S. Pat. No. 3,023,168 a heavy-duty liquid detergent composition in the form of a stable suspension is obtained using a special triethanolamine detergent salt, expensive and highly soluble potassium tripolyphosphate and sodium carboxymethylcellulose as an essential suspending agent.
Another approach to the solution of this problem is disclosed in U.S. Pat. No. 3,042,623 which uses sodium tripolyphosphate. According to this patent it is "critical" to include large amounts of ammonium sulfate; "solubility of the compositions is impaired if less than 20% of ammonium sulfate is employed."
U.S. Pat. No. 3,232,878 provides a sodium tripolyphosphate "suspension" using soap together with fatty acid alkanolamide; no sulfonate detergent is present. In this patent the solid tripolyphosphate is added to water to give a "smooth cream," presumably a suspension of solid particles of tripolyphosphate, and alkanolamide and soap (in relatively low concentrations up to 10%) are added.
U.S. Pat. No. 3,720,621 states
According to the patent, the inclusion of potassium and/or ammonium salts of inorganic or organic acids increases the solubility of the sodium tripolyphosphate builder salt. In the detergent formulations shown in the patent a hydrotrope is employed and the only alkylbenzene sulfonate detergents mentioned are the more expensive potassium alkylbenzene sulfonates.